This invention relates to methodology enabling, selectively, external, or implantable, active detection of anatomical acoustic heart-sound information. Specifically it pertains to an active method based upon: (a) utilizing a wave-generator-driven stimulator, or actuator, to stimulate mechanically, and thereby vibrate, an acoustic sensor (designed especially for capturing heart sounds, and placed externally on, or within, the anatomy) at a frequency close to the sensor's nominal, characteristic, mechanical resonance frequency; (b) observing variations in this characteristic mechanical frequency that occur over time in the sensor as a consequence of the mechanical impinging of acoustic waves, and particularly heart-sound waves; and then (c) effectively recognizing that these time-based variations may accurately and thoughtfully be interpreted as being representative of occurring anatomical acoustical activity, and in particular, heart sounds.
With this unique approach, acoustic sensitivity is very high, and so also is signal-to-noise ratio. For primary illustration purposes herein, one preferred and best-mode manner of practicing the methodology of the invention is described chiefly in the “external” placement and operational setting, wherein it has been found to offer exemplary performance.
Regarding the prior-art setting of the present invention, external electronic and acoustic transducers have been used, and are well known, to detect chest wall vibrations caused by heart sounds. Generally, passive transducer systems have been employed to detect such vibrations. These transducers typically employ any of microphones embedded in a generally bell-shaped (or other) housing, accelerometer techniques using piezoelectric and/or resistive transducers, or fully integrated medical event-monitoring systems (MEMS) devices. The techniques used in conjunction with such known devices and techniques are often limited because of less than satisfactory sensitivity and signal-to-noise-ratio behaviors associated with the transducers.
In general terms, overall prior art data-collection practice for evaluating, and even for “driving” real-time therapy and treatment of, cardio-function conditions of a subject's heart involves principally the gathering of two, different categories of data—electrical, and acoustical. For example, ECG-electrical information for diagnostic purposes, such as for providing “synchronizing” fiducial markers to understand when certain heart-activity events are occurring, as well as for other important reasons, is very well known. Known also is the fact that collected, heart-activity-produced sound (acoustical) information, i.e., heart sounds, provides extremely useful diagnostic data. With respect to the matter of heart-sound collection, since the early days of phonocardiography, the importance of gathering the so-called S1, S2, S3 and S4 heart sounds has been clearly recognized. Information-gathering practice over the years has demonstrated how electrical ECG signals and the important, heart-produced S1, S2, S3 and S4 heart-sound signals may be correlated in different ways to produce accurate, useful diagnostic information.
In all of this background, heart-related, signal-collection practice, a continuing challenge remains. It relates to achieving the clear, accurate and plainly identifiable gathering of heart sounds. The present invention focuses its attention on this issue, and does so with a featured, special and unique, “active”, rather than purely passive, methodology which may be practiced either externally, or implantably, as, for example, in association with an implanted pacemaker.
In accordance with a preferred, and best-mode, implementation of the invention, what is proposed is a method for acquiring, for various utility purposes, such as the display-presentation of accurate heart-sound data, or the establishment of a patient-treatment protocol, among others, a subject's anatomical heart-sound information involving the following basic steps:
(a) utilizing a wave-generator-driven stimulator, or actuator, to stimulate mechanically, and vibrate, an acoustic sensor (placed on or within the anatomy) at a frequency close to the sensor's nominal, characteristic, mechanical resonance frequency;
(b) observing variations in this characteristic mechanical frequency that occur over time in the sensor as a consequence of the mechanical impinging of acoustic heart-sound waves; and then
(c) effectively recognizing that these time-based variations may accurately be interpreted as being representative of occurring heart sounds.
In a more specific sense, the invention furnishes a unique, active method for acquiring a subject's anatomical heart-sound information which is useful in performing a cardio investigation, and in producing a related utility output, such as the ones briefly mentioned above, involving that subject. This method more specifically includes the steps of:
(a) placing on or within the subject's anatomy at a selected anatomical site an acoustic sensor having the form of an acoustical-to-electrical-output transducer possessing a known, characteristic mechanical resonance frequency;
(b) using a wave generator having an electrical output, stimulating (actuating) the transducer via an actuator to vibrate the transducer mechanically at a frequency which is close to its characteristic resonance frequency;
(c) coupling to a frequency and phase comparator the electrical outputs of the transducer and of the wave generator;
(d) observing over time any time-based differences which exist between the two, thus-compared outputs;
(e) interpreting such observed differences as being representations of the subject's heart sounds; and
(f) from such interpreted differences, producing a utility output associated with the subject.
The transducer and the actuator/stimulator may either be directly mechanically integrated in a unified structure, or alternatively, may be non-integrated, but used during practice of the method of the invention in what might be referred to as being in close “mechanical communication”, i.e., in close proximity to one another, as through closely adjacent contact with a subject's anatomy. While certain modest structural suggestions are made herein, it should be understood that the present invention is not concerned with the particular structural configuration(s) chosen for the transducer/actuator component, or components, and thus no special details of either are elaborated herein. Those generally skilled in the relevant art will know how to configure and implement such structures in conventional manners, both for external and internal (implanted) applications.
Preferably, the transducer is selected to possess a natural mechanical resonance frequency which lies within the known range of heart-sound frequencies (about 5-Hz to about 110-Hz). We have found that a good range to consider for this resonance frequency is about 10-Hz to about 110-Hz, and we illustrate the invention herein with an excellent choice of about 30-Hz. With this natural mechanical resonance frequency chosen for the transducer, a good, and very practical stimulation/vibration frequency has been found to be about 15-Hz. This turns out to be a frequency which resides naturally toward one side of the peak natural resonance frequency response curve, or graph, of the transducer, and “lies” on that curve at a point which is approximately centered on, and between the opposite ends of, one of the two, well-recognized, substantially linear portions of the response-amplitude curve that are disposed on laterally opposite sides of the “central” natural resonance frequency.
These and other important features and advantages offered by the methodology of the present invention will become more fully apparent as the description now follows below is read in conjunction with the accompanying drawings.